This invention relates to electron discharge devices and, in particular, to electron discharge devices having an improved structure for irradiating exterior of the device a volume having a substantial cross section and providing a discharge therein.
In recent years electron beam generating devices have been used to produce molecular excitation of a gaseous working medium. This molecular excitation is useful in producing a lasing action within an optical cavity. In addition, it may be used with advantage to provide the desired electrical conductivity of a gaseous working medium in a magnetohydrodynamic device such as a generator and accelerator. It also may be used with other devices that require or use electrically conductive or ionized gases.
An excellent example of one of the above-noted types of apparatus may be found in U.S. Pat. No. 3,702,973 entitled "Laser Ozone Generator in Which a Broad Electron Beam with a Sustainer Field Produce a Large Area, Uniform Discharge" in the name of Jack D. Daugherty et al, of common assignment with the present invention and incorporated herein by reference as if set out at length.
The Daugherty et al patent describes an electron beam generator which in one form may be briefly described for purposes of the present invention as a vacuum chamber in which a high voltage electrode accelerates a directed stream of electrons toward and through an electron beam window such as electron beam window 47 shown and described in the Daugherty et al patent. A foil or electron beam window 47 in the chamber wall provides a physical barrier to maintain the vacuum in the chamber, but is essentially transparent to the passage of electrons to permit the stream of electrons to pass from the vacuum chamber. An electrode such as electrode 52 is positioned closely adjacent the foil outside the chamber and another electrode is spaced from the first electrode to form a lasing cavity outside the vacuum chamber that may be at about one-tenth of an atmosphere to atmospheric pressure and above. A high voltage potential is applied across the electrodes 50 and 52 as shown and described, for example, in the Daugherty et al. patent and this potential, in cooperation with the electron beam, produces a discharge which molecularly excites a working gas typically flowing between the electrodes to produce in a laser a population inversion and production of a laser beam.
I have found that in prior art devices, the precluding factor for attaining electron beam uniformity is foil scattering of the emerging electrons and that this scattering is substantially independent of the accelerating voltage. I have further found that the electron beam profile across the working or interaction region is virtually independent of the electron beam generator characteristics except very near the foil. Components projecting into gas flowing through the reaction region causes turbulence which, in the case of lasers, degrades the optical quality of the laser beam.
The scattering in prior art devices of electrons by the foil results in the deposition of substantial amounts of energy in the gas in portions of the working region that are of little, if any, value.